Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof. Each standard typically dictates the type of communication, type of encoding, type of modulation, channel access protocols, data rates, et cetera, to be performed by the wireless communication devices.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera, communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channel pair (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel or channel pair. For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication session between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives an inbound RF signal via the antenna and amplifies it. The one or more intermediate frequency stages mix the amplified RF signal with one or more local oscillations to convert the amplified RF signal into a baseband signal or an intermediate frequency (IF) signal. The filtering stage filters the baseband signal or the IF signal to attenuate unwanted out of band signals to produce a filtered signal. The data recovery stage recovers raw data from the filtered signal in accordance with the particular wireless communication standard.
To ensure that data is properly transmitted and recaptured by wireless communication devices, the standard to which the wireless communication devices are compliant prescribes one or more data rates. Traditionally, the processing performed by a wireless communication device was done on a “one processing step per one clock interval” basis. As the need for greater speed of performance increased, many wireless communication devices employed parallel processing using co-processors and some further employed double edge processing.
As is known, double edge processing allows a processing device to perform one processing step on the rising edge of the clock and another processing step on the falling edge of the clock. To ensure that each processing step, i.e., the one on the rising edge and the one on the falling edge, have an equal amount of time to be completed, the processing device should be clocked by a 50% duty cycle clock. As is also known, if an imbalanced duty cycle clock is used (e.g., 60%/40% duty cycle clock), the processing of both steps must be completed during the shorter of the two portions of the clock (e.g., the 40% portion).
Because of the need for an accurate 50% duty cycle clock to improve performance of processing devices, including processing devices within wireless communication devices, many implementations of 50% duty cycle clocks have been developed. For example, a phase locked loop (PLL) may be used to produce a clock that is twice the desired clocking rate to produce the desired 50% duty cycle clock. However, PLLs are relatively complex circuits and, when implemented on an integrated circuit (IC), consume a relatively large portion of the IC real estate, which adds to the cost and power consumption of the IC.
Other 50% duty cycle clock implementations include some form of post processing or feedback processing to better control the duty cycle of reference clock. While such post processing and feedback processing provide a 50% duty cycle clock, they are relatively complex circuits and, when implemented on an integrated circuit (IC), consume a relatively large portion of the IC real estate, which adds to the cost and power consumption of the IC.
Therefore, a need exists for a 50% duty cycle clock that is readily suitable for implementation on an integrated circuit due to its minimal power consumption and economy of design.